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Action of intrauterine contraceptive devices

      To the Editors:

      The commentary by Spinnato (Spinnato JA II. Mechanism of action of intrauterine contraceptive devices and its relation to informed consent. Am J Obstet Gynecol 1997; 176: 503-6) is a selective literature review that he uses to conclude that the scientific evidence published to date is insufficient to indicate that the main mechanism of action of the copper intrauterine contraceptive device (IUD) is achieved by a spermicidal effect that prevents fertilization of the ovum. Spinnato then states that if a woman is considering this method of contraception she should be informed that there is a strong probability that the main mechanism of action of the IUD is inhibition of uterine implantation of the conceptus. This conclusion differs from the literature review conducted by several other respected groups (World Health Organization in 1987, Sivin in 1991, and Croxatto et al. in 1994), who each independently concluded that the main mechanism of action of copper IUDs was not prevention of implantation of the fertilized ovum into the uterine lining. Although the author quotes the study of Tredway et al. involving only four subjects wearing IUDs who had an absence of sperm in the oviducts, he neglects to mention the study of El Habashi et al.
      • El Habashi M
      • El-Sahwi S
      • Gawiah S
      • Osman M
      Effect of Lippes loop on sperm recovery from human fallopian tubes.
      who found no sperm in the oviducts of 30 IUD users after midcycle coitus in contrast to sperm being found in the oviducts of 14 of 30 controls. The author also fails to cite the findings of three other studies that demonstrated that copper has a direct deleterious effect on sperm motility and penetration into midcycle cervical mucus in contrast to what occurs with other metals.
      Indirect evidence indicating that the primary action of the copper IUD action is prevention of fertilization is provided by the 7-year World Health Organization study of copper IUD users, which reported that with increasing duration of use the intrauterine pregnancy rate gradually increased whereas the ectopic pregnancy rate remained low and constant.
      • World Health Organization
      The TCu380A, TCu220C, Multiload 250 and Nova T IUDs at 3, 5 and 7 years of use: results from 3 randomized multicentre trials.
      If the copper IUD does not prevent fertilization but acts primarily by preventing uterine implantation, the tubal pregnancy rate should also increase with time.
      Thus the conclusions reached by the author regarding copper IUDs are not supported by reviewing all the published data that addressed the mechanism of action of IUDs instead of the selected studies quoted in the article.
      Although the progesterone-releasing IUD may act mainly by inhibition of implantation, the copper IUD mainly acts as a spermicide preventing fertilization. Because the majority of IUDs used in the United States and Europe are copper bearing, it is necessary to differentiate the mechanism of action of these two types of IUDs.

      References

        • El Habashi M
        • El-Sahwi S
        • Gawiah S
        • Osman M
        Effect of Lippes loop on sperm recovery from human fallopian tubes.
        Contraception. 1980; 22: 549-555
        • World Health Organization
        The TCu380A, TCu220C, Multiload 250 and Nova T IUDs at 3, 5 and 7 years of use: results from 3 randomized multicentre trials.
        Contraception. 1990; 42: 141-158